Biological systems are increasingly viewed and analyzed as highly complex networks of interlinked macromolecules and metabolites. Metabolites are low molecular weight compounds (<1 kDa) involved in chemical reactions that occur inside cells of living organisms to uphold life, i.e. the process of metabolism. The chemical diversity of the metabolome, defined as the complement of all detectable metabolites, is large and includes a wide range of compound classes, e.g. carbohydrates, amino acids, organic acids, and sterols. The quantity and number of metabolites vary with changing conditions such as environment, diet and in response to disease. Significant time and money has been invested in order to investigate the relationship between metabolite alterations and biochemical mechanisms, including disease processes.
Methods for analysis of the metabolome include nuclear magnetic resonance (NMR) spectroscopy, gas chromatography (GC) and liquid chromatography (LC) coupled to mass spectrometry (MS). In addition, Fourier transform InfraRed spectroscopy (FTIR) has been used together with direct infusion mass spectrometry to analyze metabolites.
NMR and FTIR require minimal sample preparation, however, detection limits are higher compared to the MS-based techniques and elucidation of spectra composed of many metabolites can be problematic. A problem with MS-based methods is that they require complex sample preparation protocols that involve sample extraction, purification, and other work-up steps prior to sample analysis. Those preparation protocols in addition to the solvents used as part of the MS analysis destroy the native morphology of the sample, making it impossible to correlate diagnostic results with their originating source.